There are four major goals to be pursued during the next grant period: 1) Continued development of synthetic applications of the photochemistry of 2,5-cyclohexadien-1-ones to include the intramolecular 2+2 photocycloadditions of 4-(3'alkenyl and related)-2,5-cyclohexadienones, cycloadditions resulting from tandem type A + type B photorearrangements to oxyallyl zwitterions, and a remarkable new photocyclization of 4- benzyloxymethyl and related 2,5-cyclohexadienones. These asymmetric carbocyclic and heterocyclic ring constructions are expected to have broad application in organic synthesis. 2) Enantioselective total syntheses of lycorine, Erythrina, and Homoerythrina alkaloids by methodology that will incorporate near total stereoselectivity for the reduction=alkylation of a chiral benzamide; this process will serve as a solution to the stereoselective functionalization of ring C of these alkaloids. Lycorine and related Amaryllidaceae alkaloids exhibit antiviral, antineoplastic and short-term hypotensive activity and many Erythrina alkaloids possess curare-like action. 3) Enantioselective total synthesis of the Eburnamine-Vincamine and Aspidosperma alkaloids by way of a practical "asymmetric linkage" between aromatic carboxylic acids and chiral acyclic structural units. The strategy involves the utilization of a chiral ten- carbon synthetic equivalence of secologanin, the biosynthetic non- tryptophan portion of these alkaloids. Eburnamine-Vincamine alkaloids possess hypotensive activity and favorable effects towards numerous cerebral disorders. The Aspidosperma alkaloids are important primarily for their anticancer activity. The methodology to be developed in this phase of the program will have more general application to issues of acyclic stereocontrol, wherein the focus will be on asymmetric constructions that are difficult to accomplish by existing condensation and pericyclic processes. 4) Continued exploration of the synthetic potential of solid- state organic photochemistry. Here the emphasis will be on unimolecular photoreactions, where it might be possible to control regio- and stereoselectivity by substrate confinement control in the crystalline, cocrystalline, or liquid-crystalline states. The avoidance of solvent during photolysis (often at high dilution) and the potential for unique control of photoreactions are incentives for development of solid-state host systems for utilization in synthetic organic photochemistry.